Congenital Hyperextension of the Knee
Congenital hyperextension of the knee is a relatively rare deformity that varies from simple hyperextension to anterior dislocation of the tibia on the femur.
The spectrum of deformity has been classified as recurvatum, subluxation, and dislocation.
The incidence of congenital hyperextension of the knee is 1 per 100,000 live births.
Several etiologic factors have been proposed for congenital hyperextension of the knee.
Milder forms of congenital hyperextension of the knee occur in association with a breech position in utero.
Severe forms occur in the presence of muscle imbalance and/or ligamentous laxity, such as that occurring in myelodysplasia, arthrogryposis, Larsen syndrome, and oligohydramnios.
Bilateral Congenital hyperextension of the knee is almost always syndromic most commonly associated with laxity syndromes such as Larsen’s, Beals’, or Ehler-Danlos syndrome.
Ipsilateral hip dislocation and clubfoot are present 70% and 50% of the time, respectively.
The hyperextended knee deformity is obvious, but of variable severity.
In cases of subluxation, passive flexion is limited.
In the case is dislocation, there is an inability to flex the knee actively or passively.
The quadriceps tendon is often severely contracted.
A dimple or deep crease may be present over the anterior aspect of the knee.
The patella is difficult to palpate.
Those with a more severe variant are more likely to have hip dysplasia and congenital foot deformities.
Radiographs help to differentiate the mild hyperextension deformity from the more severe type with fixed anterior dislocation of the tibia on the distal femur.
Non-operative treatment should begin as soon as possible in infancy.
Treatment begins with gentle stretching.
The tibia is easily manipulated over the femoral condyle as flexion increases.
Serial casts are used to hold the knee in flexion.
This is followed by the use of removal splints to maintain flexion.
A lateral radiograph or ultrasound image of the knee can be obtained to document the anatomic restoration of the femoral-tibial articulation.
In contrast, knees with more severe subluxation or dislocations do not respond to passive stretching or splinting.
If appropriate reduction of the tibia cannot be confirmed, then closed treated should be abandoned.
Surgical treatment may be done as early as 6 months of age and includes V-Y quadricepsplasty combined with medial and lateral arthrotomies of the knee.
The long term outcome of the treatment is generally good. Those who had hyperextension or mild dislocation have the best results.
Children with more severe dislocation who required an open reduction, but did not have any other musculoskeletal problems, generally do well.
Those with bilateral deformity associated with other disorders, don’t do well.
Loss of flexion or development of a flexion contracture can compromise long term function.